Torus creation in 2.8
You first need to change your working units because this operator won't let you input values &lt; 0.01 meters (10 cm) in the fields if you keep working with meters.



The easy way



The hard way

For the sake of maths ..?

So, the major radius is the radius of the middle section of the torus, and the minor radius is the radius of the circle section of the torus if you cut through half of it radially. 

We have 


RM : Major Radius
rm : minor Radius
Re : Exterior radius (in your case, 4.7)
Ri : interior radius (1.5)


Ri = RM - rm

Re = RM + rm

&lt;=> RM = 4.7 - rm = 1.5 + rm

&lt;=> rm (minor radius) = 1.6 and RM (major radius) = 3.1

But you need to set your units correctly for this small a model.